Fuel injector assemblies are useful for such applications such as gas turbine combustion engines for directing pressurized fuel from a manifold to one or more combustion chambers. Such assemblies also function to prepare the fuel for mixing with air prior to combustion. Each injector assembly typically has an inlet fitting connected to the manifold, a tubular extension or stem connected at one end to the fitting in a typically cantilevered fashion, and one or more spray nozzles connected to the other end of the stem or housing for directing the fuel into the combustion chamber. A single or multiple fuel feed (e.g., a cylindrical tubing or a MacroLaminate structure) circuits extend through the housing to supply fuel from the inlet fitting to the nozzle or nozzle assembly. Appropriate valves and/or flow dividers can be provided to direct and control the fuel flow through the nozzle. The fuel provided by the injector(s) is mixed with air and ignited so that the expanding gases of combustion can, for example, move rapidly across and rotate turbine blades in the gas turbine engine to provide power, for example, to an aircraft. Further discussion of a multi-layered feed strip and the technique for making same are set forth in U.S. Pat. No. 6,321,541 B1 to Wrubel et al. which is also owned by the assignee of this invention and which is also incorporated herein by reference.
In typical fuel injector assembly constructions, the fuel feed is fixedly attached at its inlet end and at its outlet end to the inlet fitting and nozzle, respectively, and generally includes a coiled or convoluted portion which is designed to absorb the mechanical stresses generated by the differences in thermal expansion of the internal nozzle component parts and the external nozzle component parts during engine combustion and shut-down. In addition, the fuel nozzle is fixedly and unyieldingly mounted to the inner end of the stem or housing. Due to the insulating air space between the housing and the fuel feed, the housing grows or expands to a much greater extent than the relatively cooler fuel feed which is enveloped by the former.
At elevated temperatures, the generally “L” or mirror-image J-shaped housing generally expands over the length of the long, vertical portion of the “L”. However, since the fuel feed remains relatively cool, with reference to the surrounding housing, the fuel feed is pulled or stretched, by the housing, with the thermal differential therebetween being largely compensated by movement of the fuel feed over the short, horizontal leg portion of the “L”.
The unsolved problem with the noted prior art construction is that if the nozzle tip is unyieldingly, rigidly attached to the housing, the occurring high stresses are maximized at a transition zone between the fuel feed inner end and the adjoining nozzle end, which can result in early low cycle fatigue failure of this assembly in the general area of the noted transition zone.
Attempted prior art solutions have been directed to self-aligning fuel nozzle assemblies of the type set forth in U.S. Pat. No. 4,454,711 to Ben-Porat, wherein the self-aligning fuel nozzle is described as reducing the development of local stresses between a turbine engine swirler member and the fuel nozzle so that wear between these parts is reduced. The Ben-Porat device is basically designed to maintain the proper alignment of the swirler and fuel nozzle for any displacement of the combustor liner relative to the combustor housing during the operation of an aircraft engine, as well as for improving engine fuel efficiency by compensating for relative movement between a liner and a combustor in six degrees of freedom. Thus, the Ben-Porat device attempts to not only solve a different problem but also the proposed structural solution, as best seen in FIG. 2 thereof, is much more mechanically complex as well as much more expensive in comparison with the present invention.
Another known construction utilizes a sliding, reciprocal, translational straight-line movement between the injector nozzle and the housing and/or shroud. However, this construction can be susceptible to excessive translational movement thereof, which in turn introduces another set of problems.